1. Field of the Invention
The present invention relates to a photomask, a method of generating a resist pattern, and a method of fabricating a master information carrier for magnetically transferring an information signal onto a magnetic recording medium.
2. Description of the Related Art
At present, in order to realize smaller size and larger capacity, the recording density of a hard disk drive and other magnetic recording and reproducing apparatuses is increasing. To realize such a high recording density, the tracking servo technique of a magnetic head for recording and reproduction plays an important role. In the present tracking servo technique, information signals such as a tracking servo signal, an address signal, and a clock signal are preformat-recorded on a magnetic recording medium. A magnetic head reproduces the information signals and scans tracks accurately while confirming and correcting the position of itself. The information signals are signals used as references so that the magnetic head can scan tracks accurately. The information signals are requested to be accurately positioned and preformat-recorded on a magnetic recording medium. One of techniques for preformat-recording such information signals on a magnetic recording medium have been disclosed in Japanese Unexamined Patent Application No. 10-40544. According to the technique, the surface of a magnetic recording medium onto which information signals are to be recorded is made come into contact with the surface of a master information carrier on which a ferromagnetic thin film is formed in a pattern corresponding to information signals, and the information signals are magnetically transferred in a lump from the master information carrier onto the magnetic recording medium.
On the master information carrier used for magnetically transferring information signals onto the magnetic recording medium as described above, a pattern of a ferromagnetic thin film has to be formed in correspondence with information signals with high precision. In a method of fabricating such a master information carrier, as shown in FIG. 16A, conventionally, a resist film 2 is formed on a non-magnetic substrate 11. By evacuation 7 of air existing between the contact face of a photomask 3 and the contact face of the resist film 2, the contact faces are made come into close contact to each other. After that, the resist film 2 is irradiated with ultraviolet rays as exposure light 4 and developed, thereby generating a predetermined resist pattern 21 shown in FIG. 16B. Further, as shown in FIG. 16C, a ferromagnetic thin film 6 is formed on the resist pattern 21 and a substrate exposed face 12 and, as shown in FIG. 16D, a ferromagnetic thin film pattern 63 is generated by the lift off method.
In the conventional method, as shown in FIG. 17, particularly air in the center area hardly escapes. It causes an air gap 8 between the resist film 2 and the photomask 3 and the pattern shape varies due to diffraction 41 of the irradiated exposure light 4. For example, as shown in FIGS. 18A to 18D, in the conventional method, the resist pattern 21 has a side-wall taper 22 caused by the diffraction 41 of the exposure light 4. At the time of removing the ferromagnetic thin film 6 by the lift off method, the side-wall taper 22 causes a burror debris 61 in the side wall. As the pattern line width is becoming narrower, as shown in FIGS. 19A and 19B, the resist film 2 covered with the photomask 3 is exposed to the diffraction 41 of the exposure light 4. No pattern is generated after development, and the exposed face 12 appears in a part of the non-magnetic substrate 11.
Therefore, a main object of the present invention is to provide a resist pattern generating method useful for generating a resist pattern onto not limited to a master information carrier but the surface of a substrate widely and generally.
Another object of the invention is to provide a method of fabricating a master information carrier used for preformat-recording information signals onto a magnetic recording medium by magnetic transfer, capable of generating a ferromagnetic thin film pattern corresponding to information signals with high precision.
Other objects, features, and advantages of the invention will become apparent from the following description.
The invention is summarized as follows. A resist pattern generating method includes a first step of forming a resist film on the surface of a substrate, a second step of forming a recess for deaeration in an area where no pattern is generated and forming a projection for close contact in a pattern generating area in the surface of the resist film, a third step of making a photomask come into contact with the projection in the resist film and performing deaeration between the photomask and the resist film via the recess so as to bring the photomask and the projection into close contact, and a fourth step of irradiating the photomask with exposure light in the close contact state to expose the surface of said projection formed on said resist film to light in correspondence with a pattern shape.
According to the invention, the recess is preliminarily formed in the surface of the resist film and deaeration such as evacuation is performed via the recess at the time of pattern exposure, thereby enabling the close contact between the surface of the pattern forming area as the projection and the photomask to be made sufficiently strong. Thus, the resist pattern can be formed with precision while preventing diffraction of exposure light.
In the invention, preferably, in the second step, a plurality of recesses for deaeration are formed so as to be connected to each other in a peripheral area of the resist film.
In the invention, preferably, an almost disc-shaped substrate is used as the above-described substrate, and recesses for deaeration are formed almost radially so as to extend from a center area of the resist film to the peripheral area.